Intercommunicating system



March 28, 1944. R. H. HERRICK INTERGOMMUNIGATING SYSTEM Filed March 12,1942 INVENTOR. ROSWELL H. HERRIGK WM W M ATTORNEYS Patented Mar. 28,1944 INTERCOMMUNICATING SYSTEM Roswell H. Herrick, Oak Park, Ill.,assignor-to Automatic Electric Laboratories, Inc., a corporation 01Delaware Application March 12, 1942, Serial No. 434,339

9 Claims.

The present invention relates to telephone systems and more particularlyto improvements in intercommunicating telephone and signaling systems ofthe type in which a loudspeaker is employed at a main or master station,and the usual telephone instrument is used at each subordinate station.

It is an object of the present invention to provide an improved systemof the character described wherein the circuit apparatus is arranged inan improved manner to minimize all signal energy losses in the signaltransmission channels, and to minimize the number of line con-' ductorsused in the line interconnecting the stations.

According to another object of the invention, a separate and directbattery feed circuit to the master station transmitter is provided whichutilizes one of the voice transmission conductors and one of thesignaling conductors of the line interconnecting the stations.

In accordance with a further object of the invention, an improved.arrangement is provided for separating the battery feed circuits fromthe voice current transmission circuits in order to reduce the losses inthe voice current transmission circuits.

It is another object of the invention to provide an improved arrangementfor producing a signal at the master station each time a called stationis signaled from the master station.

According to another object of the invention, the transmission of thereturn signal to the master station is dependent upon the operation ofthe signal device provided at the station being signaled from the masterstation.

The invention, both as to its organization and method or operation,together with further objects and advantages thereof, will-best beunderstood by reference to the following specification taken inconnection with the accompanying drawing, in which the single figureillustrates an improved intercommunicating system characterized by thefeatures of the invention briefly referred to above.

Referring now to the drawing, the intercommunicating system thereillustrated comprises a 3 master station A and two subordinate stations3 and C, the three stations being interconnected by a four conductorline 22. The system may, if desired, be used to provide communicationfacilities between the lobby and the several apartments of an apartmentbuilding, in which case the equipment of the master station A is locatedin the lobby of the building and the stations B and C are located in twodifferent apartments of the building. Alternatively, the system may beused to provide communication iacilities between the oiilce of abusiness executive and the desks of his assistants.

Briefly considered, the equipment provided at the master station Acomprises a transmitter II. a loudspeaker 15, a pair of couplingcondensers l6 and H, a pair of coupling transformers l2 and IS, acurrent limiting resistor l0. and a call switch ll. Each of thesubordinate stations comprises a handset including a transmitter and areceiver 3|, a hook or cradle switch, and a buzzer 33. The systemfurther comprises a transformer which is common to the subordinatestations, and a battery 34 which is connected to supply energizingcurrent to the transmitters provided at the several stations- Separatechannels are used for transmitting voice currents to and from the masterstation A. More p ifi ly. the first and second conductors 24 and 25 ofthe line 22 define a channel for transmitting voice currents to themaster station from a called subordinate station, and the second andthird conductors 25 and 26 define a second channel for transmittingvoice currents to a called subordinate station from the master station.The first conductor 24 is also used in conjunction with the fourthconductor 23 to provide a circuit for controlling the buzzers 33b, 33c,etc.. from the master station. The fourth conductor 23 is also used incombination with the second conductor 25 to provide a circuit forenergizing the transmitter l8 provided at the master station.

In considering the operation of the system, it may be assumed that acall intended for the subordinate station B is initiated at the masterstation A. In this regard it is noted that code signaling is utilizedselectively to signal the different subordinate stations. Each time theswitch I I is operated, a circuit is completed for energizing the signalbuzzers33a, 331), etc., in multiple, this circuit extending from thepositive terminal of the battery 34 by way 'of the winding 31, theconductor 24, the contacts of the switch II, the conductor 23, thecontacts 38b, 380, etc.. and the windings of the buzzers 33b, 330, etc..in multiple to the negative terminal of the battery 34. When thusenergized, the buzzers operate to signal the subordinates at thestations B, C, etc. Since, however, the switch II is operated inaccordance with the code designating the station B, only this stationwill answer the call.

Incident to the operation of the buzzers 33, a

return signal is transmitted from the station B to station A to indicatethat the called station is being signaled. Thus, as the buzzers l2operate, the contacts 38 thereof are intermittently opened to interruptthe current flow through the winding 31 of the transformer 35. Thepulsating current thus caused to fiow through the winding 21 of thetransformer 25 causes a corresponding alternating voltage to bedeveloped by induction in the winding 30 of the transformer 35. Thevoltages appearing across the windings 36 and 31 are impressed acrossthe transformer winding IS over a circuit which includes the battery 34,the transmitters 30 in parallel, the first and second line conductors 24and 25 and the condenser IS. The resulting alternating current fiowthrough the winding l3 causes a corresponding alternating voltage to beinduced in the winding ll which is reproduced by the loudspeaker as anaudible return signal tone.

When the attendant at the station B answers the call by lifting thehandset b, Ilb from its supporting hook or cradle, circuits arecompleted for energizing the transmitters 30 and it, that for energizingthe transmitter l8 extending from. the positive terminal of the battery34, by way of the contacts 32b, the second line conductor 25, thetransmitter l8, the winding 20, the current limiting resistor ID, thefourth line conductor 23, the contacts 38 and the windings of thebuzzers 23 in parallel to the negative terminal of battery, and that forenergizing the transmitter 30b including the transformer winding 38 andthe contacts of the switch 32b. Coincident with the completion of thesecircuits the hook or cradle switch contacts 29b are closed to bridge thereceiver 3lb across the line conductors and 26. With the system thusconditioned for operation, signal current traverses the primary winding20 of the transformer I! each time the party using the master stationequipment speaks into the transmitter It. More specifically, thiscurrent fiows in a closed local circuit which includes the indicatedwinding 20, the transmitter l8 and the condenser H. A correspondinginduced voltage is developed across the terminals of the secondarywinding 2|, which voltage is applied by means of the second and thirdline conductors 25 and 26 across the terminals of the receiver Jib forreproduction. In a similar manner, when the answering party at thestation B speaks into the transmitter b, signal current traverses theprimary winding 26 of the transformer 35. A corresponding inducedvoltage is developed in the secondary winding 21 of this transformer,which is applied by means of the first and second line conductors 2| and2!, and the condenser l 8 across the input terminals of the couplingtransformer l2. This voltage also appears across the secondary winding14 of the transformer l2 and is reproduced by the loudspeaker I! at asufliciently high transmission level to be readily understood at a pointsubstantially removed from the loudspeaker. It will be understood thatwhen the conversation is terminated and the handset 30b, llb is restoredto its supporting hook or cradle at the subordinate station B, thecontacts of the hook or cradle switch'flb are disengaged to interruptthe above-traced circuits for energizing the two transmitters 20b andThe manner in which the subordinate station 0 or another subordinatestation included in the system may be called and conversational circuitsset up between this station and the master station A, will be readilyapparent in view of the foregoin explanation.

Since the signal current transmission channels as described above do notinclude amplifiers, the greatest possible efliciency is required toobtain an adequate loudspeaker volume from the signal currents suppliedby the transmitters provided at the subordinate stations, and also toobtain adequate handset receiver volume from the master stationtransmitter l 8 when it is required that this transmitter shall respondto sound waves originating at points two or three feet removedtherefrom. To obtain the required volume of reproduction at both themaster and subordinate stations the impedances between the variousconnected elements are carefully matched and the line losses are held toa minimum. I

The purpose of-providing the line conductor 23 separate from the voicecurrent transmission channels is not alone to provide a simple signalingcircuit, but also to keep direct current from traversing the handsetreceivers 3| provided at the subordinate stations. Moreover, byseparating the battery feed circuit for the transmitter II from thevoice current transmission circuits, the voice frequency currentsproduced by the transmitter l8 may be confined within the closed lowimpedance circuit including the primary winding of the transformer I9and the condenser II. By virtue of this arrangement the voice frequencycurrents developed incident to operation of the transmitter l8 are notdissipated as direct current line losses, as would be the case if thebattery feed and voice current transmission circuits were not separated.In this regard. it is pointed out that the resistor It has the functionof reducing the magnitude of the current supplied to the transmitter l8from the battery 34 to a value which is substantially less than that ofthe current supplied to the transmitter 30b, for example, as provided atthe subordinate station B. The latter transmitter may require a normaloperating current of approximately 150 milliamperes to provide therequisite output for satisfactory operation of the loudspeaker l5,whereas the optimum current for the remote pickup transmitter l8provided at the master station A is about '75 milliamperes.

While one embodiment of the invention has been disclosed, it will beunderstood that various modifications may be made therein which arewithin the true spirit and scope of theinvention.

What is claimed is:

1. In a loudspeaking intercommunicating system, a pair of stations eachincluding transmitter and receiver elements, a four conductor lineextending between said stations, the first and second conductors of saidline defining a signal channel for transmitting signal currents betweensaid stations in one direction, the second and third conductors of saidline defining a second signal channel for transmitting signal currentsbetween said stations in the other direction, and the second and fourthconductors of said line defining a circuit for energizing thetransmitter provided at one of said stations.

2. In a ioudspeaking intercommunicating system, a pair of stations eachincluding transmitter and receiver elements, a four conductor lineextending between said stations, the first and second conductors of saidline defining a signal channel for transmitting signal currents betweensaid stations in one direction, the second and third conductors of saidline defining a sec-' ond signal channel for transmitting signalcurrents between said stations in the other direction, and the secondand fourth conductors of said line defining a normally incompletecircuit for energizing the transmitter provided at one of said stations,and means at the other of said stations for completing said circuit.

3. In a loudspeaking intercommunicating system, a pair of stations 'eachincluding transmit ter and receiver elements, a four conductor lineextending between said stations, the first and second conductors of saidline defining a signal channel for transmitting signal currents betweensaid stations in one direction, the second and third conductors of saidline defining a second signal channel for transmitting signal currentsbetween said stations in the other direction, and the second and fourthconductors of said line defining a normally incomplete circuit forenergizing the transmitter provided at one of said stations, a normallyincomplete circuit for energizing the transmitter provided at the otherof said stations, and a switch at said other sta tion operative tocomplete both of said circuits.

4. In an intercommunicating system, a pair of stations each includingtransmitter and receiver elements, a 1ine connecting said stations andincluding at least four conductors, the first and second conductors ofsaid line defining a channel for transmitting signal currents betweensaid stations in one direction, the second and third conductor of saidline defining a channel for transmitting signal currents between saidstations in the oppostie direction, a signal device at one of saidstations controllable over the first and fourth conductors from theother of said stations to produce a signal indication and to produce areturn signal voltage, means including the first and second conductorsof said line for impressing said voltage across the terminals of thereceiving element provided at said other station, a normally incompletecircuit including the second and fourth conductors of said line forenergizing the transmitter provided at said other station, and means atsaid one station for completing said circuit.

5. In an intercommunicating system, a pair of stations each includingtransmitter and receiver elements, a line connecting said stations andincluding at least four conductors, the first and second conductors ofsaid line defining a channel for transmitting signal currents betweensaid stations in one direction, the second and third conductors of saidline defining a channel for transmitting "signal currents between saidstations in the opposite direction, a signal device at one of saidstations controllable over the first and fourth conductors from theother of said stations to produce a signal indication and to produce areturn signal voltage, means including the first and second conductorsof said line of the receiving element provided at said other station, anormally incomplete circuit including the second and fourth conductorsof said line for energizing the transmitter provided at said otherstation, a normally incomplete circuit for energizing the transmitterprovided at said one station, and a switch at said one station operativeto complete both of said circuits.

6. In an intercommunicating system, a pair of stations each includingtransmitter and receiver elements, a line connecting said stations andincluding at least four conductors, the first and second conductors ofsaid line defining a channel for transmitting signal currents betweensaid stations in one direction, the second and third conductors of saidline defining a second channel for transmitting signal currents betweensaid stations in the opposite direction, a buzzer provided at one ofsaid stations and controllable over the first and fourth conductors ofsaid line from the other of said stations to produce an audible signaland to produce a return signal voltage, and means including the firstand second conductors of said line for impressing said return signalvoltage across the terminals of the receiving element provided at saidother station.

'7. In an intercommunicating system, a pair of station, each includingtransmitter and receiver elements, a line connecting said stations toprovide two separate signaling channels one of which couples thetransmitter element at one of said stations to the receiver element atthe other of said-stations and the other of which couples thetransmitter element at the other of said stations to the receiverelement at said one station, a buzzer at said one station controllableover said line from said other station to produce an audible signal andto produce a return signal voltage, and means for impressing said returnsignal voltage on said one channel.

8. In an intercommunicating system, a pair of stations, a lineconnecting said stations to provide a signaling channel therebetween, abuzzer at one of said stations controllable over said line from theother of said stations to produce an audible signal and to produce areturn alternating current signal voltage, and means for impressing saidreturn alternating current signal voltage on said channel.

9. In an intercommunicating system, a pair of stations, 9. lineconnecting said stations to provide a signaling channel therebetween, asignal device at one of said stations controllable over said line fromthe other of said stations to produce a signal indication and to producea return alternating current signal voltage, and means for impressingsaid return alternating current signa1 voltage on said signalingchannel.

ROSWELL H. HERRICK.

for impressing said voltage across the temiinals-

